1. Field of the Invention
The present invention relates to a body structure of a motor vehicle, and in particular to a body structure of a motor vehicle which is provided with a structure manufactured by a tube hydraulic forming method or the like.
2. Description of the Related Art
It is conventionally known that a hollow structure is obtained by supplying high-pressure fluid such as oil into a raw tube and deforming the tube into a predetermined configuration by using a tube hydraulic forming method.
Japanese Patent Unexamined Publication No. 8-337182 discloses a body structure of a motor vehicle which is provided with two hollow structures formed by a tube hydraulic forming method. In the vehicle body structure, the two hollow structures are mutually connected along a partial area of its longitudinal direction.
Japanese Patent Unexamined Publication No. 9-150752 discloses a vehicle body frame structure that comprises a plurality of hoop-shaped members. The hoop-shaped members are obtained by extruding raw aluminum alloy into hollow members and bending the hollow members. Then, the body frame structure is formed by welding the members to make a doorframe and the like.
U.S. Pat. No. 5,269,585 discloses a motor vehicle body, which is provided with extruded hollow profiles or structures.
Similar examples of such conventional art are also disclosed in Japanese Patent Unexamined Publications No. 10-95364, No. 10-95365, No. 9-30345, No. 10-138950 and No. 8-192238.
Since a hollow structure is formed by uniformly pressurizing a raw tube from its inner side by using a tube hydraulic forming method, the, hollow structure can be made from materials such as ultra-high-strength steel. The ultra-high-strength steel has greater tensile strength than material of the conventional structure formed by press molding. As a result, since the hollow structure has greater proof stress and therefore has great strength, the weight of the vehicle body can be decreased. Accordingly, as mentioned above, many vehicle body structures provided with hollow structures formed by the tube hydraulic forming method have been proposed.
However, such hollow structures formed by the tube hydraulic forming method are not enough applied to the vehicle body structure, and various applications of the hollow structures to the vehicle body structure therefore have been demanded.
Further, the application of a hollow structure or a closed section structure made by other than the tube hydraulic forming method to a vehicle body structure also has been demanded.